Telephone-exchange system



A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILE!) N0v.2, 1917.

Patented June 8, 1920.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2, 191?.

1,342,823. Patented June 8, 1920.

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A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2, 1917.

1,342,823. Patented June 8, 1920.

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A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2. 1917.

1,342,823. Patented June 8, 1920.

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A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED may. 2, 1911.

1,342,823. Patented June 8, 1920.

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TELEPHQNE EXCHANGE SYSTEM.

APPLICATION FILED Nov. 2, 1917.

Patented June 8, 1920. I3\SHEETS-SHEET 6. Q Q R A. E. LUNDELL AND E. H.CLA'RK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV- 2,1917- Patented June 8, 1920.

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A. E. LUNDELL AND E. H. CLARK. TELEPHONE EXCHANGE SYSTEM. APPLICATIONFILED N0V.2I I917.

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A. E. LUNDELLAND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED NOV. 2, 1917.

1,342,823. PatentedJune 8,1920.

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Thausa nds A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED n0v.2,1917.

Patented June 8, 1920.

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TELEPHONE EXCHANGE SYSTEM.

APPLICAHON FILED NOV. 2, 1917.

Patented June 8, 1920.

13 SHEETSSHEET 12.

A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2. 1917.'

Patented June 8, 1920.

I3 SHEETS-SHEET 13.

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AI|BEN E. LUNDELL AND EDGAR H. CLARK, OF NEW YORK, N. Y., ASSIGNORS 'IOWESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A

CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Iatent.

Patented June 8, 1920.

Application flied November 2, 1917. Serial No. 199,888.

To all whom it may concern:

' Be it known that we, ALBEN E. LUNDELL and EnoAu H. CLARK, citizens ofthe United States, residing at New York, in the county of Bronx andState of New York, and at New York in the county of New York and Stateof New York, respectively, haveinvented certain new and usefulImprovements in Telephone-Exchange Systems, of which the following is afull, clear, concise, and exact description.

This invention relates to telephone exchange systems of thesemi-automatic type, and more particularly to systems in which tandemtrunking is required.

It is the object of this invention to provide a system in whichsubscribers calls may be extended through a plurality of offices intandem and to accomplish this end in a rapid and efficient manner.

In accordance with this object a switchin center is provided, therebeing provided at this point an operator corresponding to a B operator,who will receive calls from outlying offices and who will then operateautomatic switching mechanisms under the control of a ke set to extendthe calling line to a desire( outlying ofiice. From this outlying officethe call may be extended by means of mechanical switches, or anindicator may be operated at this point to inform the operator at thetandem point of the number of the desired line. If the call is to beagain trunked from this point through another distant office in tandem,the indicator will also inform the tandem point operator as to theoffice to which the call is to be trunked.

In the present disclosure it has been assumed that all calls will beextended to a tandem point operator who will trunk to an outlyingoffice, it being obvious that if the call is for a number located at herown office she could readily complete the connection, and that in thiscase the indication of the last office would be omitted.

No disclosure has been made of the method by which calls may becompleted at an outlying office provided with automatic switches forcompleting this type of connection, since this form of connection iswell understood in the art.

A feature of the invention is the method of providing metallicsupervision for the various operators concerned in setting up theconnection.

A further feature of the invention resides in an improved method forperforming the operations necessary in handlin the overflow condition,that is, the condition which arises when all the trunks of a selectedgroup are busy.

Another'feature of the invention resides in the provision and method ofcontrolling two allotters which control the assignment of senders to theoperator controlling the switching center.

A still further feature of the invention is provided by a novel testwhich is made by the sender to determine whether or'not the operator atthe tandem point has removed her plug from the jack, the object of thistest being to delay the operation of the impulse sending device whichcontrols the call indicating mechanism at such office until suchoperator is ready to receive a call.

An added feature of the invention is the provision of means to delayoperation of the sender, when connection is being established to aninterdistrict ofiice selector, until such selector has arrived at itsnormal position and is ready for reoperation.

A further feature of the invention is an arrangement by which thestepping relay, that is, the relay which controls the successiveoperations of the counting relays in the sender, is used only on callsto a distant office; that is, if the office selector is local, thecounting relays will be directly controlled from the commutator of theswitch being operated; but if the call is extended through aninterdistrict ofiice, the stepping relay is utilized to insure greateraccuracy.

Other features will appear from the following description and appendedclaims.

It is thought that the invention will best be understood from thefollowing detailed description, reference being had to the accompanyingdrawings.

In the drawings, Figures 1 to 13 inclusive indicate diagrammatically atelephone exchange system embodying the principles of the presentinvention. Fig. 14 is a plan showing with what relation to one anotherthe various sheets of drawings should be laced, it being understood,however, that igs. 3 and 4 are interchangeable,

switch contacts shown tended through a local 'ofiice selector or aninterdistrict oflice selector. 1

Fig. 1 shows a" calling subscribers substation and a cord circuit at anA ope'rators position, as well as the outgoing-end ofa trunk to thecordless o erators position at the switching center; ig. 2 showsthe-01rcuits of a district selector, all the sequence in this figurebeing under the control of the sequence SWICCh shown at the bottom ofthe figure, w1th the exception of the contacts withm the dotted lines,which are utilized for overflow slgnaling under the control of thesequence swltch shown in such dotted rectangle; Fig. 3 shows thecircuits of a local oflice selector; F1 4 shows the circuits of aninterdistrict o ce selector; Fig. -5 shows the circuits of an 1ncomingtrunk at a tandem pomt, together with the cord circuit of a manualoperator at an outlying oflice and the substation apparatus of a calledsubscriber; Fi 6 shows the circuits of a cord finder, w ile 1n thedotted rectangles are shown the circuits for controlling two allotters,there being a seuence switch associated with each ailotter orcontrolling thecontacts associated with it within the dotted lines;Figs. .7, 8 and 9 indicate sender circuits for re istering a desirednumber and for transmltting suitable impulses for controlling theextension of the call; Figs. 10, 11, 12 and 13 show the circuits of therelay call indicator which controls the indication of the designation ofthe desired outlying oflice and of the desired line number.

spring 19, conductor 20,

The subscriber at substation 10 desiring to initiate a call removes hisreceiver from the hook, causing a line signal to be displayed before theA operator, one of whose cords is indicated at 0. The operator onobserving this signal, inserts the plug 11 into answering jack 12associated with the line signal of the calling subscriber and inquiresthe number of the wanted line. The operator at 0 by means of an orderwire which may be of any well-known type, converses with the operator atthe switching center, whom we shall hereafter designate as the cordlessoperator, and upon being advised to use the trunk outgoing from jack 13,inserts plug 14 into jack 13 and extends the calling line to. theoperators position shown in Fig. 2., When plug 14 is inserted into jack13 a circuit is completed from grounded battery, lamp 15, resistance 17,sleeve conductors of plug 14 and 'ack 13, windingof relay 18, to ground.Iielay 18 is energized in this circuit and lamp 15 is lighted.

A circuit is now completed from ground, lower right-hand contact ofsequence switch lower windin of relay 21, lower right-hand winding 0repeatmg coil 22, armature and front contact upper ri-lght-hand wmdingofrepeating coi not shown, but

of relay 18, winding of polarized relay 23i 22, trun conductor 24, upperwindin of relay 21, upper right-hand contact 0 sequence switch spring25, to grounded battery. Flow of current in this clrcult is in such adirection as not to energize polarized rela 23, but relay 21 isenergized, completmg a circuit from ground, armature and ront contact ofrela 21, upperright-hand and lower left-han contacts of sequence switchspring 26,- lamp 27 togrounded battery. Lamp 27 is lighted to inform thecordless operator that the A operator has plugged in on the assignedtrunk. The cordess operator then momentarily depresses non-lockingassignment key 28, whereulpon a circuit is completed from groundedattery, power magnet of sequence switch 29, upper contact 0 sequenceswitch spring 30, closed lower contacts of key 28, to ground. Sequenceswitch 29 moves from osition 1 to positon 2 under the control 0 itsnormal contact 31.

It is to be observed at this point that if at the time the assi nmentkey is depressed the ,sequence switch; associated with any otherdistrict selector is standin in position 2, it will be immediately moveout of position 2 and restored to its normal position,

when the sequence switch shown in Fig. 2 arrives in osition 2. Thiswould occur as follows. he relay corresponding to relay 32 associatedwith such other selector would .be enellgized over a circuit extendingfrom and front contact of relay 32, left-hand con-.

tacts of a sequence switch spring corresponding to sequence switchspring 35, to ground. This,relay would then complete a circuit fromgrounded battery, power magnet of its associated sequence switch, lowerright-hand contact of a sequence switch sprmg corresponding to sequenceswitch spring 30,1eft-hand armature and front con-.

tact of relay 32, lower right and upper left contacts of a sequenceswitch spring corresponding to sequence switchspring 26, to ground, formoving its associated se uence switch through positions 2 and 3. T erelaly corresponding to relay 32 is deenergized w on the associatedsequence switch leaves soon as the sequence switch arrives in position6, a circuit is completed from grounded battery, power magnet of suchsequence switch, upper right-hand contact of a sequence switch springcorresponding to sequence switch spring 37, commutator segment 38,commutator brush 39 to ground, for moving this sequence switch into itsfirst or normal position.

Returning now to the regular operation of the system, when sequenceswitch 29 arrives in position 2, a circuit is completed from groundedbattery (Fig. 6), right-hand winding of relay 40, conductor 41, uppercontacts of sequence switch spring 42, conductor 43, lower right andupper left con tacts of sequence switch spring 35, to ground. Relay 40is energized in this circuit and completes a circuit fromgroundedbattery, winding of power magnet 44 of the sequence switchassociated with the cord finder, upper right-hand contact of sequenceswitch spring 45, right-hand armature and front contact of relay 40, toground, for moving this sequence switch out of position 1 and intoposition 3. WVhen sequence switch 44 leaves position 2, the originalenergizing circuit of relay 40 is broken, but this relay remainsenergized over a locking circuit extending from ,grounded battery,righthand winding of relay 40, conductors 41 and 46, left-hand armatureand front contact of relay 40, upper contact of sequence switch spring47 finder brush 48, conductor 49 and lower contact of sequence switchsprings 50 associated with undesired selectors, to ground. It is to beremembered that only one district selector sequence switch can be inposition 2 at a given time, and therefore only the district selectorwith which the sender is to be associated can be seized by the cordfinder. When sequence switch 44 arrived in position 3, a circuit wascompleted from grounded battery, winding of updrive magnet 51, lowercontact of se quence switch spring 45, right-hand armature and frontcontact of relay 40, to ground. This caused the cord finder brush set tobe moved upward in search of the terminals of the link circuit withwhich a sender is to be associated. As explained, relay 40 is main--tained energized as long as the finder is passing over the terminalsassociated with district selectors whose sequence switches are in anyother position excepting position 2. When brush 48 encounters a terminalassociated with the link circuit with which a sender is to beassociated, the locking circuit of relay 40 is broken. This relay doesnot immediatel deonergize, however, since an alternate olding circuitextends from grounded battery, left-hand winding of relay 40, right-handcontacts of sequence switch spring 52, commutator 53, brush 54, toground. When brush 54 engages an insulating segment of commutator 53, atwhich time the finder brush set will be accurately centered v ontheterminals of an idle trunk, this second holding circuit for relay 40 isbroken and this relay denergizes and opens at its right-hand contact anarmature the driving circuit of magnet 51, bringing the finder brushesto rest on the terminals associated with the desired district selector.When relay 40 is denergized, a circuit is completed from groundedbattery, winding of power magnet'of sequence switch 44, lower left-handcontact of sequence switch spring 55, to ground at the right-handarmature and back contact of relay 40, for moving this sequence switchout of position 3 and into position 4.

When the cord finder sequence switch arrives in position 4 a circuit iscompleted from grounded battery, power magnet of sequence switch 29,lower right-hand con tact of sequence switch spring 37, conductor 56,terminal 57, finder brush 58, conductor 59, lower left-hand contact ofsequence switch spring 60, conductor 61, upper left-hand contact ofsequence switch spring 62, to ground, for moving this sequence switchout of position 2 and into position 3.

0 With sequence switch 44 in position 4, a circuit is completed fromgrounded battery, right-hand winding of relay 40, upper right-handcontact of sequence switch spring 106, to ground. Relay 40 is energizedand completes a locking circuit for itself from grounded battery,right-hand winding of relay 40, conductors 41 and 46, left-hand armatureand front contact of relay 40, lower contact of sequence switch spring47, brush 107, terminal 108, conductor 109, lower left-hand contact ofsequence switch spring 50, to ground. The energization of relay 40completes a circuit from grounded battery, power magnet of sequenceswitch 44, upper right-hand contact of sequence "switch spring 45,right-hand armature and front contact of relay 40, to ground, for movingthis sequence switch out of position 4 and intoposition After thecordless operator depressed the assignment key, she depressed keys in akey set to control the registration of the desired line. Assuming thatthe desired substation is No. 8888 and is not on a party line, and

that the outlying oflice throu h which it may be reached rom the tan emointto WhlCh connection will be extende by automatic switches isrepresented by the code number 323, the operator will then depress thetandem hundreds key No. 3, a tandem tens key No. 2 and a tandem unitskey No. 3, a key N0. 8 in each of the thousands, hundreds, tens andunits columns, respectively,-and will also depress the start key 63,since no stations impulses are to be sent.

If the outlying ofiice to be reached is one to which a great many callsare to be made, it may be possible to accomplish the tandem registrationby depressing a single dis trict key indicated at 64, it being observed,

as will appear presently, that the depression of this single key willhave the same efi'ect on the registers controlling the outlying oficeselection as the depression of the tandem hundreds, tens and units keysNos. 3, 2, 3, respectively.

Assumin that the upper allotter 153 shown in ig. 6 is standing inposition 1 to assign the sender shown in the accompanying drawings, theoperation of setting the registers is as follows. As soon as the tandemhundreds key. No. 3 is depressed, a circuit is completed from groundedbattery (Fig. 7), conductor 65, winding of relay 66, winding of relay67, closed contacts of tandem hundreds key No. 3, windingof relay 68,conductor-69, conductor 70, upper right-hand contact of sequence switchspring71, winding of relay 72, conductor 73, upper lefthand contact ofsequence switch sprlng 74, to ground. Relays 66, 67, 68 and 72 areenergized in this circuit, relay 72 looking itself to ground at itsleft-hand armature and front contact. In response to the closure oftandem tens key No. 2, a circuit is completed from grounded batteryconductors 65, 75 and 76, closed contacts of tandem tens key No. 2,winding of relay 77, conductor 69, to ground over the path described. Inresponse to the operation of tandem units key No. 3, circuit iscompleted from grounded battery, conductor 78, winding of relay 79,closed contacts of tandem units key No. 3, conductors 80 and 69, toground over the path described. It is thus apparent that in response tothe setting up ofthe number 323 on the tandem keys or the depressionofdistrict key 64, relays 66, 68, 67, 77, 79 and 72 have been energized.The energization of start relay 66 completed parallel circuits for thepower magnets of the sequence switches controlling the class, districtbrush, district group, ofiice brush and ofiice group registers,respectively, it being borne in mind that the cord finder sequenceswitch is at this time in position 5. The circuit of the class registerpower magnet may be traced from ground at the armature the magnet of thearmature and back contact of relay 81,

power magnet of class register sequence switch 82, conductor 83, upper Ileft-hand contact of sequence switch spring 84, to grounded battery. Thecircuit of the power district brush register may be traced from groundat the armature and front contact of relay 66, right-hand armature andback contact of relay 85,=powe r magnet 86, conductor 87, upperright-hand contact of sequence switch spring 88, to grounded battery.The circuit of the district group register sequence switch may be tracedfrom ground at the armature and front contact of relay 66, right-handarmature and back contact of relay 89, power magnet 90, conductor 91,lower right-hand contact of sequence switch sprin 88, to groundedbattery. The circuit of %he ofiice brush register sequence switch may betraced from ground at the armature and front contact of relay 66,right-hand armature and back contact of relay 92, power magnet 93,conductor 94, upper right-hand contact of sequence switch spring 84, togrounded battery. The driving clrcuit of the office group registersequence switch may be traced from ground at the armature and frontcontact of relay 66, righthand armature and back contact of relay 95,power magnet 96, conductor 97, lower right-hand contact of sequenceswitch spring84, to grounded battery.

Under the influence of the above traced circuits, the registers arecaused to rotate from the positions they had last assumed until broughtto rest under the control of the test relays 81, 85, 89, 92 and 95,respectively, associated with them. When the class register reachesposition 8, a circuit is completed from grounded battery, conductor 65,winding of relay 81, class register spring 98 (position 8), closedcontacts of tandem hundreds key No. 3, conductors 99, 100, 101, 80, 69and 70, to ground over the path described. The energization of relay 81opens at its right-hand armature the driving circuit of power magnet 82,and this causes the class register to be brought to rest in position 8.When the district brush register arrives in position 1, a circuit iscompleted from grounded battery, conductor 65, winding of relay 85,district brush register spring 102, closed in position 1, armature andfront contact of relay 68, conductors 69 and 70, to ground over the pathdescribed; The resultant energization of relay 85 causes the districtbrush register to come to rest in position 1. When the district groupregister arrives in position 3, a circuit is completed from groundedbattery, conductor 65, relay 89, district group register spring 103,closed in position 3, armature and front contact of relay 67conducdescribed, causlng the district group register to come to rest inposition 3. When the office brush register reaches position 2, a circuitis completed from grounded battery, winding of relay 92, office brushregister spring 104, closed in position 2, armature and front contact ofrelay 77, conductors 69 and 70 to ground. The resultant energization ofrelay 92 causes the ofiice brush register to come to rest in position 2.l/Vhen the office group register reaches position 3, a circuit iscompleted from grounded battery, conductor 65, winding of relay 95,office group register spring 105, closed in position 3, armature andfront contact of relay 79, conductors 69 and 70, to ground as described,causing the ofiice group register to come to rest in position 3.

As soon as the class and district brush registers have been set, asindicated by the energization of relays 81 and 85, cord finder sequenceswitch 44 is moved from position 5 to position 6 over a circuitextending from grounded battery, power magnet of sequence switch 44,conductors 110, 111 and 112, upper left-hand contact of sequence switchspring 113, conductor 114, left-hand armature and front contact of relay81, left-hand armature and front contact of relay 85, to ground at thearmature and front contact of relay 66. As soon as the district groupregister is positioned, as indicated by the energization of relay 89,cord finder sequence switch 44 is moved outof position 6 and intoposition 7 by a circuit extending from grounded battery, power magnet ofsequence switch 44, conductors 110, 111 and 112, upper right-handcontact of sequence switch spring 113, conductor 115, left-hand armatureand front contactof relay 89 to ground at the armature and front contactof relay 66. As soon as the office brush and oflicegroup registers havebeen positioned, as indicated by the energization of relays 92 and 95,sequence switch 44 is moved out of position 7 and into position 8 over acircuit extending from grounded battery, power magnet of sequence switch44, conductors 110, 111 and 112, upper right-hand contact of sequenceswitch spring 55, conductor 116, left-hand armature and front contact ofrelay 92, left-hand armature and front contact of relay 95 to ground atthe armature and front contact of relay 66.

The method of setting the number and stations registers will now, bedescribed. As soon as start key 63 is depressed, it being understoodthat the stations. keys are so Wired that if stations impulses are to besent the depression of a stations key will perform the same startingfunction as the start key, a circuit is completed from grounded battery(Fig. 9). winding of relay 117, closed contacts of start key 63,conarmature and back contact of relay 120,

power magnet 121, conductor 122, lower left-hand contact of sequenceswitch spring 123, to grounded battery. The circuit of the unitsregister sequence switch may be traced from ground at the right-handarmature and front contact of relay 117, right-hand armature and backcontact of relay 124, power magnet 125, conductor 1126, lower right-handcontact of sequence switch spring 123, to grounded battery. The circuitof the tens register sequence switch may be traced from ground at therighthand armature and front contact of relay 117, right-hand armatureand back contact of relay 127, power magnet 128, conductor 129, upperright-hand contact of sequence switch spring 123, to grounded battery.The circuit of the hundreds register sequence switch may be traced fromground at the right-hand armature and front contact of relay .117,right-hand armature and back contact of relay 130, power magnet 131.,conductor 132, lower left-hand contact of sequence switch spring 133, togrounded battery. The circuit of the thousands register sequence switchmay be traced from geound at the right-hand armature and front contactof relay 117, right-hand armature and back contact ofrelay 134, powermagnet 135, conductor 136, lower righthand contact of sequence switchspring 133, to grounded battery. The number and stations registers; nowrotate and continue to rotate until they arrive at the positionsdetermined by the keys depressed. ,lVhen the thousands register reachesposition 8, a circuit is completed from grounded battery, conductor 137,winding of relay 134, thousands register spring 138, closed in position8, closed contacts of the thousands key No. 8, conductors 119 and 70, toground over the path described. The resultant energization of relay 134opens the driving circuit of the power magnet 135 and the thousandsregister is brought to rest in position 8. By means of similar circuits,relay 130 is energized in position 8 of the hundreds register to causethis register to stop in such position. Similarly, relay 127 causes thetens register to stop in position 8 and relay 124 causes the unitsregister to stop in position 8. When the stations register arrives inposition 0, a circuit is completed from grounded batens ,to assignanother sender.

tery, tvinding of relay 120, stationsre 'ster spring 139, closed inposition 0, close contacts of start key 63, conductor 140, normalcontacts of stations key No. 1 -(used to indicate the 10,000 digit .whenthe number of the desired line is more than 10,000), conductor 119, toground over the path described. The resultant energization of .relay 120causes the stations register to come to rest in position *0. As soon asall the number registers and stations register have been positioned, asindicated by the energization of their associated controlling relays134, 130, 127, 124, 120 respectively, a circuit is completed for movingsequence switch 44 out of position 8 and into position 9, this circuitextending from grounded battery, power magnet of sequence switch 44,conductors 110, 111, lower right-hand contact of sequence switch spring55, conductor 141, in series through the left-hand armatures and frontcontacts of the re lays 134, 130, 127, 124 and 120 respectively, toground at the right-hand armature and front contact of relay 117.

With the cord finder sequence switch in position 9, parallel circuitsare completed to the key release magnets 142, 143, 145, 146 and 147 inparallel, these circuits being traceable from, grounded battery, upperlefthand contact of sequence switclr spring 88, conductor 148, windingof magnet 142, to ground; also from grounded battery, lower eft-handcontact of sequence switch spring 88, conductor 149, winding of magnet147. to ground; also from grounded battery, upper left-hand contact ofsequence switch spring 133, conductor 150, through the windings ofmagnets 143 and 145 in parallel to ground; and from grounded battery,upper right-hand contact of sequence switch spring 133, conductor 151,winding of magnet 146, to ground. The magnets 142, 143, 145, 146 and 147control the release of all the keys which have been depressed, and thesekeys should now be released. If all the keys are successfully released,the locking circuit of relay 72 will be broken when the last key isreleased, and this relay will deenergize, completing a circuit formoving sequence switch 44 out of position 9 and into position 10, thiscircuit extending from grounded battery, power magnet of sequence switch44, conductors 110, 111 and 112, lower right-hand contact of sequenceswitch spring 113, lower contact of sequence switch spring 152,left-hand armature and back contact of relay 72, to

I ground.

With sequence switch 44 in position 10, a circuit is completed foradvancing the upper allotter sequence switch 153 into a position This isaccomplished by means of a circuit extending from grounded battery,power magnet of sequence switch 153 conductors 154, 155, 156, lowercontacts ofi sequence switch spring 42, conductors 157, 158, lowercontact of sequence switch spring 159, conductor 160, left-hand contactsof sequence switch spring 161 associated with the bottom allotter 163,the upper right-hand contact of spring 162, closed in the normalposition of the foot clutch, to ground.

' It might be well'to' describe at this time the interaction of the twoallotters which assign senders, these allotters being of the sequenceswitch type, one being indicated at 153 and the other at 163. Assumingthat in the beginning allotter 163 was resting in position 18and thatallotter 153 was in position 1, upon the completion of the operation upto the point described, allotter 153 will be advanced out of position 1andinto position 2, as described. In position 2 of allotter 153, acircuit is completed from grounded battery, resistance '169, upperleft-hand contact of sequence switch spring 71, winding of relay 72,upper right-hand contact of sequence switch spring 159, conductor 160,to ground over the path described. If one of the three finders which isassigned by allotter 153 is idle and in a position to beassigned, relay72 is not energized in this circuit, since it will be shunted by acircuit extending from grounded battery, resistance 169, upper and lowerleft-hand contacts of sequence switch spring'71, conductor 170, upperright-hand power magnet of sequence switch 153, conductor 154, uppercontact of sequence switch spring 152, to ground at the armature andback contact of relay 72.

As long as all the cord finders are busy and until one of them is readyfor allotment, as indicated by its arrival in position 18, no keys canbe depressed, since relay 72 by its energization supplies battery to therelease magnet conductors 148, 149, 150, 151 by way of allotter spring171 and the right-hand armature and front contact of relay 72, andtherefore no number can be set up on the operators key set until asender has been assigned. As soon as a sender becomes idle, relay 72 isshunted and the allotter is moved out of position 2 and into position 3,as described.

Provided that the manually operable" key 164 associated with allotter153 is in its normal position, the allotter will at once he moved out ofposition 3 and into position 6 by means of a circuit extending fromgrounded battery, power magnet of allotter 153, upper right-hand contactof sequence switch spring 165, normally closed contacts of key 164, toground. In position 6 the I allotter assigns the next sender and afterthis sender has been operated, is moved into position 12 bysimilarcircuits to those just described. After this third sender hasbeen used, the allotter is moved into position 17 by means of circuitsjust described. When allotter 153 arrives in position 17, a circuit iscompleted from grounded battery,- winding of the power magnet ofallotter 163,

upper left-hand contact of sequence switch spring 166, lower left-handcontact of se quence switch spring 167, to ground, for moving allotter163 out of position 18 and into position 1, whereupon it will assign itsfirst sender which we shall refer to as the fourth sender. IVithallotter 163 in position 1, a circuit is completed from groundedbattery, power magnet of allotter 153, lower left-hand contact ofsequence switch spring 165, upper right-hand contact of sequence switchspring 168, to ground, for moving this allotter out of position 17 andinto position 18. where it will rest until allotter 163 has assigned itslastsender and moved into position 17, whereupon allotter 153 will bemoved out of positionl8 and into position 1, to reassign the firstsender.

The cord finder sequence switch remains in position 18 after completingits operation and awaits reassignment. The cord finder shown in thedrawing is to be allotted in position 1 of allotter 153. Therefore, withsequence switch 44 in position 18 and allotter in position 1, a circuitis completed from grounded battery, power magnet of sequence switch 44,conductors 110, 111 and 112, lower left-hand contact of sequence switchspring 113, conductor 158, lower left-hand contact of sequence 'switchspring 159, conductor 160,

left-hand contacts of sequence switch spring 161, to ground at thenormal contact of the foot clutch 162. This moves sequence switch 44into position 1 ready for operation when another district sequenceswitch moves into position 2. In case the allotted cord finder is busy,in which case its sequence switch will not be resting in position 18,the operation will be delayed until it arrives in some position between9 and 18. In positions 10 to 17 of the cord finder sequence switch whichwould normally be the next to be allotted, a circuit is completed fromgrounded battery, power magnet of allotter 153, conductors 15-1, 155 and156, lower contactsof se quence switch spring 42, conductors 157, 158,lower left-hand contact of sequence switch spring 159, to ground overthe path described, which would move the allotter from position 1 toposition 2, and it would then advance into position 6, as described, toassign the next cord finder.

Assuming that it is desired to eliminate the senders assigned byallotter 153, these senders can be cut out of service by depressinglocking key 164, it being further assumed that at the time this key isdepressed allotter 153 is standing in position 1. The allotter may thenbe moved out of position 1 as usual and will not effect the operation ofthe first sender. The allotter stops in position 3 and allows allotter163 to become independent; that is, to reassign senders 4, 5 and 6. Inthis case, with the key 164 depressed, lamp 172 has a circuit extendingfrom grounded battery, operated contacts of key 164, resistance 173, thenormal contact of the foot clutch spring 174, resistance 175, lamp 172,to ground, but it is shunted by a path extending by way of resistance176, conductor 177,-lower right-hand contact of sequence switch spring106, to ground. When the assigned cord finder sequence switch arrives inposition 18, this shunting circuit is removed and lamp 172 is lighted.At this point the foot clutch, controlling springs 162 and 174, isoperated. In this case, ground contact supplied from the lowerright-hand contact of clutch spring 162 and conductor 178 to the lowerright-hand contact of allotter spring 166 prevents allotter 163 fromstopping in either positions 17 or 18, and therefore this allotter willkeep on assigning senders Nos. 4, 5 and 6. When the foot clutch isoperated, the allotter 153 associated with it is ineffective, becausethe ground feed at the upper right-hand contact of clutch spring 162 isopen. The allotter 153 may now be revolved and any tests or repairswhich it was desirable to make may be made without affecting the operation of the system. When the allotter 153 is to be again out intoservice, it must beleft in position 18. Key 164 may now be released andlamp 172 will not be lighted until allotter 163 is in some positionincluded in the positions 1 to 14. This circuit extends from groundedbattery, normal contacts of key 164, conductor 179, upper and lowerrighthand contacts of allotter spring 161, conductor 180, lower andupper contacts of allotter spring 181, resistance 182, lower contact ofclutch spring 174, resistance 175, lamp 172, to ground, causing thelighting of this lamp. At this time the foot clutch may be restored toits normal position, and the allotter 153 will be moved out of position18 and into position 1 when allotter 163 arrives in position 17, asusual. The circuits of the locking key and foot clutch associated withallotter 163 are identical with those described for allotter 153.

In case both allotters get into a position for assigning senders; thatis, in case both these allotters are in a position included betweenpositions 1 and 14, neither is effective and an alarm is given. Thealarm circuit extends from ground, lower left-hand and upper rigl1t-handcontacts of sequence switch spring 183, conductor 184, normal contactsof key 164, upper and lower right-hand con-

